I've been moving forward on solving my oven spring problems at the bakery. Last week, I used a combination of techniques, and was more satisfied with the loaves than I have been by any so far. They're still not perfect, but I did get a complement from a Swiss man. Bread complements from Europeans really count.
After some reading, I concluded that the problem was, as I suspected, the fan in the oven, which was drying out the surfaces of my bread before it had a chance to expand, keeping the crumb tight and doughy and causing frequent and unsightly blowouts. The fan can't be turned off while the oven is on, but based on the comments of others facing similar issues on the Fresh Loaf forum, I tried a few things to mitigate it. The three basic techniques were: using very wet dough (I made successful Pane Genzanese), overheating the oven and then actually turning it off for a few minutes after the dough went in (scary, and probably would be more successful if baking on a hearth or stone), and covering the loaves with mixing bowls for the first 20 minutes or so of baking. The last option, although kind of time consuming and odd, works pretty well on the dual principle of protecting the loaves from the wind, and allowing them to steam themselves within the small space. The crusts weren't as crispy as if I had steamed them properly in the oven, and the method is kind of awkward, but the results were encouraging to say the least.
Last week I made Pane Genzanese, challah, oatmeal sunflower seed, and Hamelman's Vermont sourdough (now Brooklyn Sourdough), both plain and with pecans and raisins. I added a touch of extra commercial yeast to the raisin doughs to help support them.